Conversion of high molecular weight petroleum feeds to more valuable products by catalytic processes such as fluidized catalytic cracking is important to petroleum processes. In the fluidized catalytic cracking process, higher molecular weight feeds are contacted with fluidized catalyst particles in the riser reactor of the fluidized catalytic cracking unit. The contacting between feed and catalyst is controlled according to the type of product desired. In catalytic cracking of the feed, reactor conditions such as temperature and catalyst circulation rate are controlled to maximize the products desired and minimize the formation of less desirable products such as light gases and coke.
In the current economics of modern refining, as lighter, easier to convert feedstocks are in increasingly lesser availabilities and higher pricing, refiners are continually moving to ways in which to process the more challenged or “heavier” feedstocks that are more available and can be purchased at a discount as compared to the lighter hydrocarbon feedstocks. These heavier feedstocks tend to have lower API gravities (i.e., denser) and higher viscosities than the lighter hydrocarbon feedstocks. This makes these heavy oil feedstocks, including gas oils and vacuum tower bottoms typically fed to an associated fluidized catalytic cracking (or “FCC”) unit more difficult to convert to high value products such as gasoline, and require a higher “conversion rates” in order to reduce the amount of heavy hydrocarbons products, i.e., those products with a boiling point above about 430° F. (221° C.), generated from the cracking process and higher yields of gasoline product.
With the advance of zeolitic cracking catalysts with greatly improved cracking activity, most modern fluidized catalytic cracking reactors utilize a short contact-time cracking configuration. With this configuration, the time in which the catalyst and the fluidized catalytic cracker feedstream are in contact is limited in order to minimize the amount of excessive cracking which results in the increased production of less valued products such as light hydrocarbon gases as well as increased coking deposition on the cracking catalysts. Short contact-time riser reactor designs are relatively new to the petrochemical industry, but have gained wide-spread acceptance and use in the industry due to the ability of optimizing hydrocarbon cracking products and yields in conjunction with the use of modern cracking catalysts.
Conventional FCC catalysts have used type Y zeolites as part of their composition. Type “Y” zeolites are of the faujasite (“FAU”) framework type which is described in Atlas of Zeolitic Framework Types (Ch. Baerlocher, W. M. Meier, and D. H. Olson editors, 5th Rev. Ed., Elsevier Science B.V., 2001) and in the pure crystalline form are comprised of three-dimensional channels of 12-membered rings. The crystalline zeolite Y is described in U.S. Pat. No. 3,130,007. Zeolite Y (see U.S. Pat. No. 3,130,007) and improved Y-type zeolites such as Ultra Stable Y (“USY” or “US-Y”) (see U.S. Pat. No. 3,375,065) not only provide a desired framework for shape selective reactions but also exhibit exceptional stability in the presence of steam at elevated temperatures which has resulted in this zeolite structure being utilized in many catalytic petroleum refining and petrochemical processes. Additionally, the three-dimensional pore channel structure of the faujasite framework zeolites, such as the Y-type zeolites, in combination with their relatively good ability to retain a high surface area under severe hydrothermal conditions and their generally low cost to manufacture makes these zeolites a preferred component for Fluid Catalytic Cracking (“FCC”) catalysts in petroleum refining and petrochemical processes.
In a pure zeolite crystal, the pore diameters are typically in the range of a few angstroms in diameter. Y-type zeolites exhibit pore diameters of about 7.4 Angstroms (Å) in the pure crystal form. However, in manufacture, defects in the crystalline structure and in particular in the inter-crystal interfaces occur in the crystalline structure of zeolites, including the Y-type zeolites. Additionally, due to certain methods of preparations and/or use, both wanted and unwanted structural modifications can be made to the zeolite crystal. It is these “defects” which lead to specific properties of the zeolite which may have beneficial properties when utilized in catalytic processes. Conventional Ultra Stable Y (USY) zeolites prepared by mild steam calcination, as taught by U.S. Pat. No. 3,375,065, contain significant amounts of mesopores in the 30 to 50 Å regions. These pores with pore diameters in the 30 to 50 Å range are herein defined as “Small Mesopores”.
What are needed in the industry are improved catalysts which have improved heavy improved heavy oil conversion rates as well as improved gasoline yields and lower undesired coke production. In particular, what are needed in the industry are improved fluidized catalytic cracking (“FCC”) catalysts that exhibit these properties. Even more preferably desired is fluidized catalytic cracking (“FCC”) catalysts that are easy to manufacture that can be used in existing short contact time FCC units with little or no modifications required to the existing unit that exhibit improved conversions and gasoline production properties.